The Theramidi

The Theramidi is a new musical device, based on the  Theremin, which produces a MIDI signal relative to the movement of objects to or away from it. The MIDI output is controlled by the intensity of light falling onto two Light Dependent Resistors (LDRs). One LDR determines the note frequency and the other can be programmed to control  a variety of MIDI effects eg Volume, Modulation etc. (see Table 1).

So the instrument can be played by moving your hands in front of both LDRs and so controlling the output pitch and volume etc.

The resistance depends on the amount of light falling on it and this variable resistance is converted by a PIC 16F877 microcontroller into a MIDI  signal which can be pre-programmed as in Table 1.

The Circuit schematic diagram is available in GIF format.

The Circuit layout is available in GIF format.

The PIC 16F877 for the TheraMIDI Unit is available pre-programmed.

The programmable TheraMIDI Unit utilizes:

• A Printed Circuit Board (PCB), 
• A pre-programmed 16F877 PIC,
• A programme switch and associated LED,
• A programmable 4-way DIP switch  which selects the Effect and Mode of operation, (See Table 1) in programme mode,
• The  4-way DIP switch which selects the MIDI transmit channel via DIP switches 1-4 (See Table 2)  
• Screw terminal sockets for connecting the LDRs,
• The power-on LED,
• A 9 volt battery connector
• A MIDI 5-pin DIN output socket,
• Screw terminal sockets for connecting the variable sensitivity control potentiometers for different light conditions

The programmable TheraMIDI unit requires:

• A 9v battery or equivalent power source

There are two modes of operation:

1. Programme Mode
2. Normal Mode

Programme Mode is entered by having Programme switch  ON at power-on. Normal Mode is entered by having the Programme switch OFF at power-on.

Programming the unit:

At power-on, if the programme  switch is simultaneously ON, then the unit will enter programme mode. The 4-Way DIP switch positions are read and stored in the EEPROM, and the unit  will operate as shown in Table 1.

Programming the Light to MIDI Unit only has to be done once and the switch positions are stored internally in the EEPROM and the unit will continue to operate in this mode, even when power is removed, until reprogrammed.

If a different controller value is required, at any time, then the programming procedure can be repeated.

Program Mode:

1. Set programme switch to ON and DIP switches 1 to 4 to the required MIDI Controller value (See Table 1)
2. Switch unit On, the power-on and programme LEDS are on.
3. Now set  operation mode via DIP switches 1-4 
4. Set programme  switch to OFF and programme LED will be off.
   

Normal Mode:

1. Set programme switch to OFF and set MIDI channel via DIP switches 1-4  (See Table 2)  
2. Now switch the unit on, the power-on LED is on and the programme LED is off.

Operation Mode:

Operation mode is set via DIP switches 1-4 (See Table 1)  in programme mode which allows the unit to produce linear/logarithmic etc. responses to the movement of an object (e.g. a hand) blocking the light falling onto the LDR.

TOM SCARFF
1 Martello Court
Portmarnock
Dublin
Ireland.

Phone: 353-1-8462160
Email: tscarff@eircom.net